The present invention relates in general to telephonic voice communication switching, and in particular, to conferencing wherein telephone conversation between two or more parties is possible. As is well known to those skilled in the art, many techniques of a wide range of complexity are used to achieve telephone conference connections. In analog systems, 3-party conferences are frequently implemented by bridging the third party across an existing 2-party circuit, while complex conference circuits are reserved for large conferences.
The advent of pulse code modulation (PCM), digital voice transmission, and switching systems has stimulated the development of new conferencing techniques which operate directly on the digital representation of voice. One important reason is that in PCM systems, the simple technique of connecting the third party to an existing 2-party call does not result in meaningful addition in mixing of the three digital signals as it does in the analog case, and thus, in the digital implementation some sort of algebraic operation is required even for small conferences. Conferencing techniques may be classified as additive or switched, and analog and digital mechanizations may be found in the prior art for both approaches.
In the additive technique, each conferee receives the algebraic sum of the signals of the other conferees. In the switch technique, an attempt is made to discover which conferee is the speaker. The speaker's signal alone is then sent to the other conferees, while the speaker may receive either a zero signal or the signal from the previous speaker. Alternatively, in a new approach, a speaker may be selected for each conferee from the traffic offered by the others, excluding that conferee's own signal. In this scheme, the actual speaker hears some "speaker" chosen from the idle conferees. The disadvantage is that a line with a high noise level will be selected over a voice line of low level.
U.S. Pat. Nos. 3,958,084 and 3,699,264 disclose conference circuits utilizing techniques for selecting the loudest speaker.